The present invention relates to a magnetoresistance effect element detecting the change of an external magnetic field, a magnetoresistance effect head equipped with the magnetoresistance effect element, a magnetic reproducing apparatus mounting the magnetoresistance effect head, and further a magnetic laminate having two ferromagnetic layers the magnetization directions of which cross approximately perpendicularly.
Hitherto, for reading magnetic information recorded in a magnetic recording medium, a method of relatively moving a reproducing magnetic head having a coil and a recording medium and detecting the voltage induced to the coil by the magnetic induction generated at the case has been used. Thereafter, a magnetoresistance effect element (hereinafter, referred to as an MR element) reproducing magnetic information by utilizing a magnetoresistance effect that the electric resistance of a specific ferromagnetic substance changes in response to the intensity of an external magnetic field was developed (see, IEEE MAG-7, 150 (1971), etc.). The MR element is used for a magnetic field sensor as well as is used as a magnetoresistance effect head (hereinafter, referred to as MR head) mounted on a magnetic reproducing apparatus such as a hard disk drive, etc.
Recent efforts have been made to obtain small size and increased capacity in a magnetic recording medium mounted on a magnetic reproducing apparatus. However, the relative speed of a magnetic head for reproducing and a magnetic recording medium at information reading becomes slower, and the expectation to obtain an MR head capable of obtaining a large output even with a slow relative speed has been increased.
For such an expectation, a very large magnetoresistance effect film has been developed. The very large magnetoresistance effect film is a multilayer film, or so-called artificial lattice film formed by alternately laminating ferromagnetic metal films and non-magnetic metal films, such as Fe/Cr and Fe/Cu, and antiferromagnetically-coupling the adjacent ferromagnetic metal films [see, Phys. Rev. Lett., 61, 2474(1988); Phys. Rev. Lett., 64, 2304(1990), etc.]. However, because in the artificial lattice film, the magnetic field required for saturating the magnetization is large, the artificial lattice film is not suitable as a film material for the MR head.
On the other hand, there is reported an example that a large magnetoresistance effect is realized in the MR film of a multilayer film composed of a ferromagnetic metal layer/a non-magnetic metal layer/a ferromagnetic metal layer formed by holding the non-magnetic metal layer between the upper and lower ferromagnetic metal layers, wherein the two ferromagnetic metal layers are not magnetically-coupled (non-coupling). The MR film has the feature that the magnetization (spin) of one ferromagnetic metal layer is fixed and the magnetization of the other ferromagnetic metal layer is magnetization-inverted by an external magnetic field. Thereby, by changing the relative angles to the spin directions of the ferromagnetic metal layers disposed holding a non-magnetic layer between them, a magnetoresistance effect is obtained, whereby such an MR element is called a spin valve element (see, Phys. Rev. B 45, 806(1992); J. Appl. Phys. 69, 4774(1991), etc.).
Although the rate of change of the magnetoresistance of such a spin valve element is small as compared with the artificial lattice film, because the magnetic field required for saturating the magnetization is small, the element is suitable for the use of MR head, and the element has already been practically used.
A general spin valve element has a laminated structure of a ferromagnetic free layer, an intermediate non-magnetic layer, a ferromagnetic pin layer, and an antiferromagnetic layer. The magnetization of the ferromagnetic pin layer adjacent to the antiferromagnetic layer is fixed to one direction under an external magnetic field by an exchange bias magnetic field from the antiferromagnetic layer. On the other hand, the ferromagnetic free layer can be freely rotated to an external magnetic field and the parallel/anti-parallel state of the magnetizations of the ferromagnetic free layer and the ferromagnetic pin layer can be easily realized in a low magnetic field. In addition, when the magnetizations of both the ferromagnetic layers are in a parallel state, the electric resistance of the element is low, and when the magnetizations are in an anti-parallel state, the electric resistance becomes high. In the spin valve element, by increasing the difference of the two resistance values, high magnetoresistance effect amplitude is obtained.
When the spin valve element is practically used, to obtain a high susceptibility by utilizing the linear region of the resistant change, it is preferred to apply a bias such that the magnetization of the ferromagnetic free layer crosses the magnetization of the pin layer at about a right angle in a zero magnetic field. The bias is also important in the meaning that the magnetization of the free layer becomes a simple magnetic domain so that Barkhausen noise is not generated in the case of rotating the magnetization of the free layer to an external magnetic field. A hard magnetic film having the same function as a magnet is formed at the side surface of the spin valve film for forming a single magnetic domain in the magnetic layer.
When the thickness of the hard magnetic film is same as the thickness of the ferromagnetic free layer, a proper bias can be applied and when the thickness of the hard magnetic layer is thinner than the above-described thickness, the formation of the simple magnetic domain of the ferromagnetic free layer is hard to attain due to an insufficient bias. Also, when the thickness of the hard magnetic film becomes thicker than the thickness of the free layer, the bias becomes excessive, whereby the permeability of the ferromagnetic free layer is lowered.
However, under present conditions, when the thickness of the hard magnetic film is thinned to a thickness the same as that of the ferromagnetic free layer, because the joining area of both the members becomes small, magnetic joining cannot be made well, and thus, the hard magnetic film must be made thicker than the thickness of the ferromagnetic free layer. As the result thereof, a bias applied to the ferromagnetic free layer becomes excessive, whereby the permeability of the ferromagnetic free layer is lowered to give a loss to the susceptibility and the output.
For solving these problems, a spin valve element employing the construction that an antiferromagnetic layer of a definite form is laminated to the end portion of the free layer to fix the magnetization of the end portion of the free layer by the exchange coupling of the antiferromagnetic layer and the free layer, and a bias is applied from the portion to the central magnetic field response portion of the free layer is proposed. Because the construction is a bias method using the antiferromagnetic layer worked in a definite form (pattern), the construction is called a patterned bias structure.
A slant view of a spin valve element of the patterned bias structure is shown in FIG. 1A. The spin valve element has a first antiferromagnetic layer 1, a ferromagnetic pin layer 3, an intermediate non-magnetic layer 5, and a ferromagnetic free layer 7 successively laminated from below, and further has a pair of second antiferromagnetic layers 9 laminated to both ends of the ferromagnetic free layer 7 in the lengthwise direction and a pair of lead electrodes 11. Both ends of the ferromagnetic free layer 7 and the ferromagnetic pin layer 3 are applied with the magnetization of uni-directional anisotropy in FIG. 1A by the magnetic exchange coupling of each of the second antiferromagnetic layers 9 and the first antiferromagnetic layer 1. That is, both end portions (oblique line portions) of the ferromagnetic free layer 7 laminated with the second antiferromagnetic layers 9 are magnetization fixed in the left-to-right direction in the figure by the exchange coupling of both members and function like a hard magnetic film. Also, the magnetization of the central magnetic field response portion held between both end portions has a magnetization of uni-directional anisotropy in the direction of the arrow in a zero magnetic field, from the bias magnetic fields of both end portions of the second antiferromagnetic layer 9 and the ferromagnetic free layer 7. On the other hand, the magnetization of the ferromagnetic pin layer 3 is fixed to a direction from the front surface to the back surface of the paper shown in FIG. 1A by the exchange coupling with the first antiferromagnetic layer 1.
In the patterned bias structure, the two exchange coupling films of the exchange coupling film of the second antiferromagnetic layer 9 and the ferromagnetic free layer 7 and the exchange coupling film of the first antiferromagnetic layer 1 and the ferromagnetic pin layer 3 become necessary. The impartation of uni-directional anisotropy to ferromagnetic layers of the exchange coupling films is carried out by a heat treatment in a magnetic field since the magnetizations of the ferromagnetic pin layer 3 and the ferromagnetic free layer 7 are each directly influenced, a heat treatment must be applied while applying different magnetic fields to each of the antiferromagnetic layers 1 and 9. When the blocking temperature of the first antiferromagnetic layer 1 wherein the exchange coupling magnetic field with the ferromagnetic pin layer 3 becomes zero is TB1 and the blocking temperature of the second antiferromagnetic layer 9 wherein the exchange coupling magnetic field with the ferromagnetic free layer becomes zero is TB2, the heat treatment process (time-temperature) is shown in FIG. 1B. In addition, because the antiferromagnetic films have a uniaxial anisotropy, a two-direction arrow for the sake of convenience shows the magnetization states.
For completely carrying out the magnetization fixing by the first and second antiferromagnetic layers 1 and 9, two kinds of antiferromagnetic layer materials having a large blocking temperature difference |Tb1-Tb2| become necessary and further, two kinds of antiferromagnetic layer materials showing a small dispersion of the exchange coupling magnetic field to the extent of not overlapping the exchange coupling magnetic fields of both members become necessary. Furthermore, in addition to these conditions, the materials having both the high exchange coupling magnetic field and the characteristics of the high blocking temperature, which are essentially important in the case of using the spin valve element cannot easily be found.
On the other hand, in the three layer structure of CoFe/Mn/CoFe, etc., by an epitaxial growth, the magnetic right-angle cross coupling between the two ferromagnetic layers CoFe is observed (see. J. Appl. Phys. 79 (8), Apr. 15, 1996, etc.).
The present invention provides a novel magnetoresistance effect element made under these circumstances and particularly provides a magnetoresistance effect element, a magnetoresistance effect element head, a magnetic reproducing apparatus, and a magnetic laminate at a low production cost.
That is, the first aspect of the invention provides a magnetoresistance effect element having a first antiferromagnetic layer; a first ferromagnetic layer which is a ferromagnetic layer exchange coupled to the first antiferromagnetic layer and has a magnetization in a first direction; a magnetization-coupling layer laminated to the first ferromagnetic layer; a second ferromagnetic layer laminated to the first ferromagnetic layer via the magnetization-coupling layer and has a magnetization of a direction crossing at about a right angle to the first direction by magnetization-coupling to the first ferromagnetic layer by the magnetization-coupling layer; an intermediate non-magnetic layer; a third ferromagnetic layer which is laminated to the second ferromagnetic layer via the intermediate non-magnetic layer and has a magnetization of an about the same direction as the first direction in the state that an external magnetic field is zero; and a second antiferromagnetic layer exchange coupled to the third ferromagnetic layer.
Also, the second aspect of the invention provides a magnetoresistance effect element having a first ferromagnetic layer having magnetization in a first direction; an inserted layer having a mixed phase film containing at least two kinds of oxides of the same metal each having a different valence number, or a laminated film formed by laminating at least two oxide layers of the same metal each having a different valence number, and laminated to the first ferromagnetic layer; a second ferromagnetic layer formed by laminated onto the first ferromagnetic layer via the inserted layer and having a magnetization in the direction crossing at almost a right angle to the first direction; an intermediate non-magnetic layer; and a third ferromagnetic layer laminated to the second ferromagnetic layer via the intermediate non-magnetic layer and having a magnetization in about the same direction as the first direction in the state that an external magnetic field is zero.
In each of these magnetoresistance effect elements, the second ferromagnetic layer and the third ferromagnetic layer holding the intermediate non-magnetic layer in the state that an external magnetic field is zero have the magnetizations which are in a crossing relation at about a right angle to each other when an external magnetic field is zero. Also, the magnetization direction of the first ferromagnetic layer and the magnetization direction of the second ferromagnetic layer are coupled in a crossing direction at about a right angle by the magnetization-coupling layer or the insertion layer. Accordingly, the magnetization directions of the first and third ferromagnetic layers can be oriented almost in the same direction, whereby a heat treatment step for imparting a magnetic bias can be reduced and thus the production process can be simplified.
In addition, such a simplification of the process largely contributes to the improvement of the productivity of magnetic heads, and the magnetoresistance effect heads and further magnetic reproducing apparatus each having a low cost can be provided.
For the magnetic bias to the first and third ferromagnetic layers, in addition to the exchange coupling bias using the first and second antiferromagnetic layers mentioned in the first aspect of the invention, a hard magnetic layer, a laminated film of plural ferromagnetic layers, a laminated layer of a ferromagnetic layer and a non-magnetic phase, a laminated film of an antiferromagnetic layer and a ferromagnetic layer, and a laminated film of a hard magnetic layer and a ferromagnetic layer can be used in place of the antiferromagnetic layer.
Also, to impart the magnetic bias, freedom is obtained in the selection of these same-quality materials. For example, when an antiferromagnetic layer is used to impart the magnetic bias, it becomes unnecessary to form a difference in the blocking temperatures of two antiferromagnetic layers and the materials can be properly selected from well-known materials, such as IrMn, PtMn, FeMn, NiMn, NiO, xcex1xe2x80x94Fe2O3, etc.
In the magnetoresistance effect element, the magnetoresistance effect head, and the magnetic reproducing apparatus of the invention, it is preferred to have the following constitutions.
1) The second ferromagnetic layer is a magnetization-free layer changing magnetization direction with a change in an external magnetic field, and the third ferromagnetic layer is a magnetization spin layer wherein the magnetization direction is not substantially changed by the external magnetic field by which the magnetization of the above-described magnetization free layer is changed. In this case, the magnetization of the first ferromagnetic layer may rotate with the change of the magnetization direction of the second ferromagnetic layer or may not rotate. In addition, the second and third ferromagnetic layers can be magnetically non-coupling with each other.
2) The third ferromagnetic layer is a magnetization free layer changing magnetization direction with a change in an external magnetic field, and the second ferromagnetic layer is a magnetization pin layer wherein the magnetization direction is not substantially changed in the external magnetic field by which the magnetization of the magnetization free layer is changed. In this case, it is preferred that the magnetization of the first ferromagnetic layer is not substantially changed in the external magnetic field by which the magnetization of the magnetization free layer is changed. In addition, the second and third ferromagnetic layers can be magnetically non-coupling with each other.
3) The first antiferromagnetic layer is laminated onto both end portions of the first ferromagnetic layer in the lengthwise direction, and/or the second antiferromagnetic layer is formed on both end portions only of the third ferromagnetic layer in the lengthwise direction.
4) The first antiferromagnetic layer is formed covering one whole surface of the first ferromagnetic layer.
5) A non-magnetic layer is further formed between the first antiferromagnetic layer and the first ferromagnetic layer or between the second antiferromagnetic layer and the third ferromagnetic layer.
6) The first, second, and third ferromagnetic layers have two ferromagnetic layers and an antiferromagnetic coupling interlayer antiferromagnetically magnetization-coupling these layers. The two ferromagnetic layers which are antiferromagnetically coupled and the interlayer constitute a unit called a synthetic antiferromagnetic film and because the two ferromagnetic layers turn an anti-parallel direction. The magnetic field is closed in the unit, whereby the magnetic field leakage to the outside can be reduced and also a bias point can be suitably controlled.
7) The magnetization-coupling layer or the inserted layer has a mixed phase film containing at least two kinds of the oxides of the same metal each having a different valence number, or a laminated film formed by laminating at least two layers of the oxides of the same metal each having a different valence number. In this case, the oxides of the same metal each having a different valence number are:
7-1) selected from FeO, Fe3O4, xcex1xe2x80x94Fe2O3, and xcex3xe2x80x94Fe2O3;
7-2) selected from CrO, Cr2O3, CrO2, Cr2O5, CrO3, and CrO5;
7-3) MnO and MnO2.
8) The magnetization-coupling layer or the inserted layer is an insulating layer made of an oxide, etc., and by further having new insulating layers holding an intermediate non-magnetic layer between them together with the magnetization coupling layer, the element, etc., of the invention has a construction wherein an electron specular reflection is induced at the interface of each insulating layer and the reflected electron returns again to the interface with the intermediate non-magnetic layer. The electron-reflecting layer is known as a specular effect.
9) When an external magnetic field is applied, the first and second ferromagnetic layers cross-coupled with each other by the magnetization coupling layer or the inserted layer causes following two kinds of magnetizing rotations by the selection of materials, etc.:
9-1) The right angle-cross coupling is cut, the exchange coupling of the first ferromagnetic layer and the first antiferromagnetic layer is maintained, and the second ferromagnetic layer only causes a magnetizing rotation.
9-2) The right angle-cross coupling is maintained and by cutting the coupling of the first ferromagnetic layer and the first antiferromagnetic layer, the magnetizations of the first and second ferromagnetic layers are rotated with an external magnetic field.
In addition, the magnetoresistance effect head of the invention may comprise:
10) a so-called shield-type head wherein the magnetoresistance effect element is disposed in the magnetic gap in the vicinity of the opposite surface of the medium of the magnetic head. Thinning the antiferromagnetic layer increases the dispersion of the exchange coupling magnetic field of the exchange coupling film but because according to the invention, it becomes unnecessary to avoid the occurrence of overlapping of dispersions, film thinning of the antiferromagnetic layer can be easily realized. Such thinning of the antiferromagnetic layer is suitable for narrowing the gap of the shield-type magnetoresistance effect head and has an effect of contributing to the increase of the density thereof.
11) a yoke-type magnetoresistance effect head wherein the magnetoresistance effect element is disposed apart from the opposite surface of the medium, and having magnetic yokes transmitting a signal magnetic field from the medium to the magnetoresistance effect element by extending from the opposite surface of the medium to the magnetoresistance effect element. In the magnetoresistance effect element of the invention, because the number of times for the heat treatment of the bias impartation can be reduced, a uniform magnetic anisotropy becomes hard to be imparted to the yoke portion and an efficient introduction of a magnetic flux from the opposite surface of the medium to the magnetoresistance effect element is expected.
Also, the third aspect of the invention provides a magnetic laminate composed of a first ferromagnetic layer having a magnetization of a first direction; a second ferromagnetic layer having a second magnetization of a direction crossing at about a right angle to the magnetization of the first direction; and a mixed phase film which is an interlayer film formed between the first and second ferromagnetic layers, and has a mixed phase film containing at least two kinds of oxides of the same metal each having a different valence number or a laminate layer containing at least two oxide layers of the same metal each having a different valence number.